NIPPV apparatus function to supply a patient with a supply of clean breathable gas (usually air, with or without supplemental oxygen) at a therapeutic pressure or pressures, at appropriate times during the subject's breathing cycle. The therapeutic pressure is also known as the ventilation pressure.
NIPPV apparatus typically include a flow generator, an air filter, a mask, an air delivery conduit connecting the flow generator to the mask, various sensors and a microprocessor-based controller. The flow generator may include a servo-controlled motor and an impeller. The flow generator may also include a valve capable of discharging air to atmosphere as a means for altering the pressure delivered to the patient as an alternative to motor speed control. The sensors measure, amongst other things, motor speed, gas volumetric flowrate and outlet pressure. The apparatus may optionally include a humidifier in the air delivery circuit. The controller may include data storage capacity with or without integrated data retrieval and display functions.
In this specification, NIPPV apparatus will be referred to “as assisted ventilation devices” which, in the broadest form, need not include all of the component features mentioned above.
Assisted ventilation devices are used for the treatment of many conditions, for example respiratory insufficiency or failure due to lung, neuromuscular or musculoskeletal disease and diseases of respiratory control.
Common to all forms of assisted ventilation is the need to control the pressure being applied to the patient. It is a known prior art technique to detect the peak pressure and compare it against a maximum threshold value. If the threshold value is exceeded an alarm state occurs, and corrective action may be taken. This corrective action can be a short-term reduction in supplied pressure, followed by an increase back to the previous pressure.